Helical path plasma



Nov. 12, 1963 "3,110,843

0. DU P. DONALDSON HELICAL PATH PLASMA Filed May 27, 1960 v ewer? SUPPLYPlasma Ouf /22 INVENTOR C'o/em an du Dana/dam;

BY M w z V ATTORNEY United States Patent 3,110,843 HELICAL PATH PLASMAColeman dn 1?. Donaldson, Princeton, NJL, assignor to Thompson RamaWooldridge lne, Cleveland, Ohio, a corporation of @hio lFiled May 27,1960, Ser. No. 32,252 6 Claims. ((31. 315-111) The present invention isdirected to a device and method for accelerating electrically conductiveplasmas.

In recent times, there has been some study made of producing electricbody forces on electrically conductive fiuids. In essence, systems ofthis type involve subjecting the electrically conductive fluid to thecombined action of electrical magnetic fields. The electric body forceinvolved is derived from the vector product of the current and themagnetic field strengths and is perpendicular to both of these vectors.The body force per unit volume of these vectors, normal to each other,is given by the vector equation:

F=jB

where F is the body force, j is the current density vector,

and B is the magnetic flux vector.

proved plasma accelerator which reduces skin friction and heat transfereffects.

Another object of the invention is to provide a plasma accelerator whichis extremely compact.

Still another object of the invention is to provide an improved methodfor accelerating a plasma in a controllable manner.

The acceleration parameter for the devices of the present invention isexpressed as follows:

Where a is the acceleration parameter,

a is the electrical conductivity of the accelerated fiuid, m is the massflow per unit area,

B, is the magnetic flux density in the z direction, and

s is the distance in the direction of plasma motion.

With the devices of the present invention, relatively large accelerationparameters are obtained with relatively limited magnetic fields, dueprimarily to the configuration provided for the plasma acceleratingpath.

A further description of the present invention will be made inconjunction with the attached sheet of drawings in which:

FIGURE 1 is an exploded view, partly in cross section, illustratingschematically a type of plasma accelerator coming within the presentinvention; and

FIGURE 2 is a modified form of the accelerator.

As shown in the drawings:

In FIGURE 1, reference numeral 16 indicates generally a magneticallypermeable core, having a helical groove 11 formed therein. The groove 11receives a helically wound conductor 12 which closes off the outerperiphery of the groove 11, and provides a helical channel 13 which:forms the acceleration space for the fluid plasma. In the form of theinvention illustrated, the plasma enters the device at the uppermost endof the helical channel 13 and emerges at the lowermost end, as indicatedby the legend on the drawing. Electrically See insulating spacers 14 and16 are provided to insulate the conductor 12. from the walls of the core10.

The apparatus of the present invention is applicable to any electricallyconductive medium such as a plasma consisting of ionized gas. Generally,the fluids employed will have a conductivity on the order of 5 mho percentimeter. Since air, even at elevated temperatures has a relativelylow conductivity, it is desirable to improve this conductivity byseeding the air stream prior to its acceleration with an ionizablesubstance such as sodium or potassium. A potassium content as little as0.1% is eilective to increase the conductivity of the air verysubstantially and render it readily usable in the process and apparatusof the invention.

The core 10 is disposed between a pair of opposed magnetic pole faces 17and 18 which'provide the axial magnetic lines of flux, identified atnumeral 19 in the drawings. The pole faces 17 and '18 are energized bymeans of leads 21 and 22 from a suitable power supply 23. A typicalvalue for the magnetic fiux density employed is on the order of 1 Weberper square meter.

An electrical field is provided between the inner radial surface of theconductor 12 and the core 10 by connecting the conductor 12 by means ofa conductor 24 to the power supply 23, and connecting the core 10* tothe power supply 23 by means of a conductor 26. Since the conductor 1-2is otherwise insulated from the core 10, the electrical field extendsacross the channel 13 in a radial direction. Hence, there are providedahnost mutually perpendicular magnetic and electrical fields which actupon the plasma during its passage through the helical path 13. Arepresentative value for the applied electrical field strength is on theorder of 400 volts per centimeter.

In some instances, it is not practical to provide large electromagneticpoles to achieve the flux densities required. For this type ofapplication, the structure of FIGURE 2 will be employed. That structureconsists of a magnetically permeable core 31 having a helical groove 32therein defining a channel 33 for the fluid plasma. A helical conductor34 is received between insulators 36 and 37 and closes oil the outerperiphery of the groove 32.

In the form of the invention illustrated in FIGURE 2, the magnetic fieldis provided by one or more turns of a coil 38 which surrounds theperiphery of the core 31. The coil 38 is energized by means ofconductors 39 and 41 from a power supply 42. When energized, the coil 38provides a magnetic field illustrated by the magnetic lines of force 43.

The electrical field perpendicular to the magnetic lines of force '43 isprovided by connecting the conductor 34 and the core 31 throughconductors 4-4 and 46, respectively, to the power supply 42.

With the devices illustrated, many operational advantages can beachieved. Due to the way in which the current flows into and out of thedevice, there is little or no net twist of the magnetic field in passingthrough the device. Furthermore, in the device, there is a tendency forthe plasma to be pinched somewhat away from the horizontal surfaces,thus reducing skin friction and heat transfer efiects.

Furthermore, the devices of the invention make it possible to tailor thestrength of the magnetic field in the axial direction, as well as bycontrolling in the axial direction, the driving radial electric field,thereby making it possible to optimize the acceleration of the plasma.In addition, the devices, particularly that illustrated in FIGURE 2 arevery compact. i

It should be evident that various modifications can be made to thedescribed embodiments without departing from the scope of the presentinvention.

I claim as my invention:

1. A plasma accelerator comprising means for proas viding a helical pathfor the plasma, means for establishing a magnetic field axially of saidhelical path, and means for establishing an electrical field atapproximately a right angle to said magnetic field.

2. A plasma accelerator comprisin a magnetically permeable core, saidcore having a helical groove therein, means for introducing anelectrically conductive fluid plasma into one end of said helicalgroove, means for withdrawing accelerated plasma from the other end ofsaid helical groove, means for creating a magnetic field axially of saidcore, and means for establishing an electrical field at right angles tosaid magnetic held.

3. A plasma accelerator comprising a magnetically permeable core, saidcore having a helical groove therein, means for introducing anelectrically conductive fiuid plasma into one end of said helicalgroove, means for Withdrawing accelerated plasma from the other end ofsaid helical groove, an electrical conductor disposed in said groove inspaced relation to the base of said groove, means insulating saidconductor from said core, and means for creating a magnetic fieldaxially of said core.

4. A plasma accelerator comprising a magnetically permeable core, saidcore having a helical groove therein, means for introducing anelectrically conductive fluid plasma into one end of said helicalgroove, means for withdrawing accelerated plasma from the other end ofsaid helical groove, a pair of electromagnetic pole faces abutting theopposed ends of said core to provide a magnetic field axially of saidcore, and means for establishl ing an electrical field at right anglesto said magnetic field.

5. A plasma accelerator comprising a magnetically permeable core, meansproviding a helical channel along the periphery of said core, means forintroducing an electrically conductive plasma into one end of saidchannel, means for Withdrawing the accelerated plasma at the other endof said channel, a coil surrounding the periphery of said core, meansfor energizin said coil to provide a magnetic field axially of saidcore, and means for establishing an electrical field through said coreat right angles to said magnetic field.

6. A plasma accelerator comprising a magnetically permeable core, meansproviding a helical channel along the periphery of said core, means forintroducing an electrically conductive plasma into one end of saidchannel, means for Withdrawing the accelerated plasma at the other endof said channel, a coil surrounding the periphery of said core, meansfor energizing said coil to provide a magnetic field axially of saidcore, a conductor received in said channel in electrically insulatedrelation from said core, and means for applying an electrical fieldbetween said conductor and said core.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PLASMA ACCELERATOR COMPRISING MEANS FOR PROVIDING A HELICAL PATHFOR THE PLASMA, MEANS FOR ESTABLISHING A MAGNETIC FIELD AXIALLY OF SAIDHELICAL PATH, AND MEANS FOR ESTABLISHING AN ELECTRICAL FIELD ATAPPROXIMATELY A RIGHT ANGLE TO SAID MAGNETIC FIELD.